Carb cleaning - adjustment on 12PT9 chipper

chas045(7b)April 7, 2012

I have a 6 year old 12PT9 MacKissic chipper (B&S Intek 9 HP engine with a Nikki carb) that had been running well until my recent start when it stumbled with choke off. It ran moderately well with just a slight choke. I had assumed that my main jet was probably clogged and I managed to remove the carb. After bowl removal, I found a very clean carb with a newer design that I am not familiar with. It has some molded plastic parts that contain the needle valve and surround the main pipe into the bowl. The pipe appeared to be completely clean. I blew air on the few openings I could approach. I didn't use carb cleaner because it looked so clean and also because I noticed that one of the main gaskets appeared to be slightly offset suggesting an air leak. Admittedly, the offset should have been there for the six good running years. I made my own gasket replacement.

Upon reinstallation without major improvement, I realized that this carburator appears to have no adjustments. Anyone have experience with these Nikki carbs or better ideas on cleaning or adjustment or something else?

Just about anything goes with a Walbro carb. Nikki's need to be handled w/ a watchful eye.The plastic parts do fine w/ carb spray, the rubber seals and float valve not so much. In my experience w/ the small Nikkis, if there is any question on fuel flow, replace the float valve kit w/ the bowl gasket. It is easier on the rider versions to monitor your flow as you can unscrew the solenoid in the bottom of the carb- but I'm guessing you have no solenoid or center plug -correct? Had you noted an internal gasket or a mounting gasket that had been distorted? Model and code could be helpful here as well.

The engine is 204412-0114-E1. I have the link to the exploded view for this engine. The carb view is on page 4.
I had been thinking of soaking the metal part in carb cleaner (you know the nasty stinky stuff that seems like it would eat through its own can, not spray) but I was sure that the rubber seals would need to be removed and I didn't know what stuff might be deep inside. Even the obvious seals are delicate molded complicated ones and I was a little nervous about even removing them.

I don't have a center plug on the bowl and it is all manual. I guess the kit is a good idea. It would also give me a replacement mounting gasket. I had never seen a needle valve in its own removable plastic housing before.

Goes back to the Nikki's work well when they work! They are good carbs, but need that extra respect. Soaking, if you have the solution then great. Otherwise, it doesn't sound as though you need to. If you know the main jet is clean above- you should be ok w/ the kit. Or if the Walbro is available....

I like to update when I have success. Even when it's a year later; and I don't know what I really did.

I have been using my chipper on occasion but in a slightly choked mode. Today I opened the carb. again and it was as clean as before. I blew air thru all obvious openings as before. The only variation, was that the molded float cartridge did not easily release from its float bowl. I knocked it on a flat surface from each side of the bowl and it finally released BUT in addition it knocked loose what I guess is the main jet that had been set in the bottom of the molded float cartridge. It appeared clean but I was able to remove a little film and possible crud that did not appear to block the hole but may have modified the slight taper surrounding both sides of the jet. I reset the jet and reassembled the carb. and the engine ran fine.

I am obviously not certain that the jet removal was the actual solution. Perhaps the third time is the charm. Or just a little air in just the right direction or.....but anyway, its working.